In optical switching and processing systems using arrays of light beams and arrays of devices with optical inputs or outputs, it is often necessary to direct several arrays of light beams onto the same surface of a device. A key problem that arises is to achieve this result without substantial loss of optical power and without introducing optical aberrations.
One technique that has been used to direct multiple arrays of light beams onto a target surface is to use a patterned, or so-called "space-variant," mirror, in which the reflectivity of the mirror varies in space. One array of light beams is arranged so that the light beams strike portions of the mirror that are highly transmissive. This first array of light beams passes through the mirror to strike the target surface. The other array of light beams is arranged to reflect from the mirror and onto the target surface. An imaging lens often is required to image the mirror plane onto the surface. Passing the beams through an image plane, however, introduces undesirable optical aberrations which limit the size of the array. Moreover, use of an imaging lens increases the distance required between the space-variant mirror and the target surface, and thus increases the overall system size.
Another technique for combining arrays of light beams is referred to as "pupil plane combination."In this technique, a first array of light beams is transmitted through one half of the pupil plane of a lens and a second array of light beams is transmitted through the other half of the lens pupil plane. This technique, however, is susceptible to large optical aberrations due to lens imperfections.
Thus, it would be desirable to provide a method for combining arrays of light beams which minimizes susceptibility to optical aberrations, which results in a compact system, and which minimizes optical power loss.